Conventionally, a ball screw device is known which includes a dust-proof member for preventing intrusion of foreign materials such as dust, grit, and waste into a nut. As such a ball screw device, a ball screw device having a configuration in which attachment of a dust-proof member to a nut is carried out by fixing the dust-proof member with a fixing screw inserted from the outer circumference side of the nut is also known (for example, see PTL 1).
In general, a ball screw device used as a mechanical element for converting rotational movement into straight movement includes a screw shaft and a cylindrical nut disposed on the outer circumference of the screw shaft, and plural balls are combined into a space between a spiral ball rolling groove formed on the outer circumferential surface of the screw shaft and a spiral ball rolling groove formed on the inner circumferential surface of the nut.
In such a ball screw device, when foreign materials such as dust attached to the surface of the screw shaft intrudes into the nut, the smooth rolling movement of the balls is hindered and thus a dust-proof member in contact with the surface of the screw shaft is often attached to an end portion of the nut.
An example of the ball screw device including the dust-proof member is described in PTL 2. In the ball screw device, as illustrated in FIG. 25, a seal-attachment large-diameter step portion 2053 is formed on both end portions of a nut 2052 screwed to a screw shaft 2050 with balls 2051 interposed therebetween. A screw hole 2054 in the diameter direction open to the inner circumferential surface of the large-diameter step portion 2053 is formed in both end portions of the nut 2052. That is, one or two screw holes 2054 in the radius direction are formed to pass from the outer circumferential surface 2052a of the nut 2052 and a flange circumferential surface (not illustrated) to each large-diameter step portions 2053. By fitting a seal 2055 into the large-diameter step portion 2053 and fastening a fixing screw 2056 to the screw hole 2054, the seal 2055 is fixed in the circumferential direction and the axis direction.
The ball screw device used as a mechanical element for converting rotational movement into straight movement generally includes a screw shaft and a cylindrical nut disposed on the outer circumference of the screw shaft, and plural balls are combined into a space between a spiral ball rolling groove formed on the outer circumferential surface of the screw shaft and a spiral ball rolling groove formed on the inner circumferential surface of the nut.
In such a ball screw device, when foreign materials such as dust attached to the surface of the screw shaft intrudes into the nut, the smooth rolling movement of the balls is hindered and thus a dust-proof member being in contact with the surface of the screw shaft is often attached to an end portion of the nut.
In the ball screw device described in PTL 2, there is a room for improvement, since the nut 2052 is provided with the screw hole 2054, a labor required for formation of the screw hole may lower a production yield. Particularly, in forming of the screw hole 2054, when the thickness of the nut 2052 is large, a drill hole as well as a tapping hole having an internal thread formed therein needs to be formed. Thus a deviation in labor or time required for the formation is widely varied, and there was a room for improvement.
Therefore, the inventors of the present invention have invented a ball screw device in which an engagement groove is formed in the circumferential direction on the inner circumferential surface of a nut with a predetermined distance from an end in the axis direction and which includes a dust-proof member in which an engagement piece formed on the outer circumferential surface thereof to have a tubular shape is elastically deformed to engage with the engagement groove and to seal a clearance between the screw shaft and the nut.
In such a ball screw device having the above-mentioned configuration, one or more grooves are formed in the axis direction on the outer circumferential surface of the dust-proof member. Accordingly, when extracting the dust-proof member, the screw shaft is inserted into a through-hole of the dust-proof member to press the inner wall of the groove toward the central axis by the use of a protrusion of a tool to disengage the engagement piece from the engagement groove.